If I am reading this correctly, you are able to access a corporate discount through your employer's corporate TA which uses GetThere. You should not be able to replicate that fare anywhere else outside your organization's enrolled TA. That is part of your employer's contract with UA and the TA.

This is both to prevent fraud (employees booking personal travel using corporate rates unless the contract permits it) and to make sure that as part of the contract, the back office work is being done by the TA.

Why are you trying to replicate the fares when you have a perfectly functioning portal?